Only when he failed in the final exam ____up his mind to study harder to catch up with the classmates ahead of him.
____ has finished the task ahead of time will be rewarded, though we don’t know who it will be.
The changes in our chemistry lab will cost quite a lot, ____ they will save us money in the long run.
Living things are dying out quickly. Let’s ask ____ destroying them in the past years.
____ that I’m feeling all right, my brain is also beginning to work much better.